Ubuntu Family
I would like to add that in meantime, Ubuntu has became available for free download as part of a Google Webfonts project.
It contains extended Latin, extended Cyrillic and extended Greek character sets.
Standard family now has 4 weights + 4 true italics:
http://www.google.com/webfonts/specimen/Ubuntu
Condensed (one weight only):
http://www.google.com/webfonts/speci...untu+Condensed
Monospaced (2 weights + 2 true italics):
http://www.google.com/webfonts/specimen/Ubuntu+Mono